The opening line of the poem gets a stanza to itself, and can be read as a kind of thesis statement: "nobody loses all the time." In other words, even the unluckiest person has some luck once in a while.
But this statement immediately starts to sound ironic in light of what follows. The speaker starts telling the story of their Uncle Sol, "who was a born failure." So this will be a poem about someone who loses most of the time, at least. The question is whether this man is a total loser, or whether even he scores a victory now and then. Right away, then, the opening claim becomes ambiguous, and by the end of the poem, the reader is left to judge whether it's true or false.
In the speaker's telling, it's not that Uncle Sol was totally hapless. In fact, he had a knack for singing and performing. He "could / sing" the old comic song "McCann He Was A Diver" like nobody's business—or, as the speaker colorfully puts it, "like Hell Itself." He would sing this song "on Xmas Eve," presumably to entertain friends and relatives. "Nearly everybody" who saw these performances thought that "he should have gone / into vaudeville"; that is, he should have tried to make a career performing in variety shows. ("Vaudeville" was a kind of theater that combined singing, dancing, comedy skits, and more, popular in the late 19th and early 20th centuries.)
Of course, the word "nearly" qualifies the claim a little bit. Obviously, there's a difference between amusing family members around the holidays and entertaining thousands on stage. And even people who respect Sol's talent aren't sure he could have made it in show business. They just suspect he could have gone further in it than in the work he actually chose—which, as the rest of the poem explains, was farming, a career at which (to put it mildly) he did not succeed.
Here it may be relevant that the nickname "Sol" is usually short for "Solomon," a name associated with wisdom (as in the biblical King Solomon). If the name is meant as an allusion, the fact that Sol keeps bumbling into folly and "failure" gives it an ironic tinge.
By line 6, the poem's general form, or formlessness, is clear. It's written in sprawling free verse that suits the speaker's chatty, energetic style. Its many enjambments (e.g., "named / Sol") make the speaker's narrative style sound almost breathless. One line spills into another, unpunctuated, with no consistent logic to the line breaks, as if the speaker is too exuberant to pause or organize their thoughts.